1. Field of the Invention
The present invention relates to a new and improved flange seal. In particular, the present invention relates to flange seals suited for use with high-pressure devices such as a chromatography pump.
2. Description of Related Art
High-pressure liquid chromatography (HPLC) generally requires the components of a sample to be separated or analyzed be dissolved in a mobile phase liquid, termed an eluent, and conveyed by that liquid to a stationary phase, that is, a chromatography column. HPLC eluent delivery systems are used to supply the liquid and deliver the liquid, with dissolved sample, to the column. Selected pressures ranging from substantially atmospheric pressure to pressures on the order of thousands of pounds per square inch are common to force the liquid into the column. Specially designed HPLC pumps are used to withstand extreme pressures and to deliver the liquid at precisely controlled flow rates in a smooth and uniform manner.
HPLC pumps are generally piston pumps. The pump head of an HPLC pump often utilizes a special high-pressure seal through which a reciprocating piston extends. For example, as shown in FIG. 2, a pump includes a pump head 31 and a reciprocating piston 32 that extends through pump head 31. Piston 32 also extends and reciprocates in a direction along the center line of piston 32 through a conventional seal generally indicated by the numeral 36. Such conventional seals generally include a seal body 37 through which piston 32 extends. An O-ring 38 is provided to seal against an inner cavity wall 41 of pump head 31 as shown in FIG. 2.
Disadvantageously, the configuration of conventional seals can lead to abrasion and granulation of O-ring 38. In particular, as the HPLC operates, piston 32 reciprocates and causes the working fluid within the pump to pressurize and depressurize, which may cause O-ring 38 to move back-and-forth, or side-to-side as viewed in FIG. 2. Such movement of O-ring 38 causes the O-ring to chafe against inner cavity wall 41 thus causing abrasion, granulation and/or other wear of the O-ring, which in turn, may lead to contamination of the working fluid and/or the mobile phase flowing through the pump. In particular, O-ring 38 may be formed of a fluoropolymer material and the introduction of such particles into the flow stream through the pump can lead to fluorine contamination of the chromatography system utilizing such a conventional seal. In addition, the O-ring may contain ionic or organic contaminates that can leach out into the fluid stream.
Other conventional pump seals are constructed with an inert polymeric ring containing an energizing internal component that transfers compressive force to the pump head and the pump piston. Exemplars of such conventional pump seals are U.S. Pat. Nos. 4,453,898, 4,260,342 and 4,173,437 which show a dual-piston reciprocating pump assemblies.
A wide variety of materials have been used for both the polymeric ring and the energizing internal component but most commonly, the inert polymeric ring for HPLC applications utilize a fluoropolymer such as polytetrafluoroethylene (PTFE) or TEFLON® while the energizing internal component is typically either a stainless-steel spring or an elastomeric O-ring. Disadvantageously, pumped fluid may contact the energizing internal component either directly or indirectly under normal operating conditions.
Accordingly, the particular material of the energizing seal component must be chosen depending upon the pumped fluid flowing through the HPLC pump. For example, a stainless-steel energizing spring is suitable for use with nonpolar pumped fluids such as methylene chloride or hexane. Stainless-steel, however, is not suitable for use with acidic aqueous pumped fluids as such fluids may cause corrosion of the spring and contamination of downstream chromatographic components. Similarly, elastomeric materials, which may be chosen for corrosive aqueous pumped fluids, are largely incompatible with relatively nonpolar solvents such as methylene chloride, tetrahydrofuran (THF) or hexane. Such solvents extract impurities, which can result in a significant decrease in the performance of chromatographic device, which in turn, may lead to high background levels for isocratic conditions and spurious peaks under gradient conditions. The cleanest and least problematic O-ring materials are typically very expensive flow polymer based O-rings. Consequently, pumping systems require a variety of different pump seals which must be changed when switching from one solvent to another thus adding considerable complexity which may compromise pump maintenance and/or considerable added expense.
What is needed is an improved high-pressure seal that overcomes the above and other disadvantages of known seals.